Practical Programming in Tcl & Tk, Third Edition

Constructing Code with the list Command

It can be tricky to assemble a command so that it is evaluated properly by eval. The same difficulties apply to commands like after, uplevel, and the Tk send command, all of which have similar properties to eval, except that the command evaluation occurs later or in a different context. Constructing commands dynamically is a source of many problems. The worst part is that you can write code that works sometimes but not others, which can be very confusing.

Use list when constructing commands.

The root of the quoting problems is the internal use of concat by eval and similar commands to concatenate their ...